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Offering a new standard for gerrymandering to the Supreme Court

November 2nd, 2015, 2:58pm by Sam Wang

Today, I filed a friend-of-the-court brief in the Harris v. Arizona Independent Redistricting Commission case (S. Ct. 14-232). The brief can be found here (for a summary of other briefs, see the Arizona Eagletarian blog). In it, I argue that the Supreme Court should reject Harris’s case on the grounds that there was no partisan injury.

Claims of partisan gerrymandering are sometimes wielded fairly loosely. Harris et al. claim that voters of one party (in their case, Republicans) were packed into districts by the Commission to impair their representation. My brief describes how such a claim can be put to an impartial mathematical test. In fact, there was no partisan asymmetry to what the Commission did. Ironically, my analysis finds a slight (but statistically nonsignificant) partisan tilt favoring Republicans, who are the complainants in this case.

The test I proposed is a simple one: the difference between the average support for a party in a state, and the median district-by-district outcome. The average-median difference* has well-known statistical properties, and can be applied to any statewide districting scheme. It might be useful in the future as a general standard for statewide partisan gerrymandering. A need for such a standard for partisan asymmetry has been expressed in the Vieth v. Jubelirer and LULAC v. Perry cases.

I have written more generally on rigorous measures of partisan symmetry. A current version of my article, “A Three-Prong Standard for Partisan Gerrymandering,” is available at SSRN.

* The average-median difference has also been proposed by Michael McDonald (SUNY Binghamton) and collaborators. My own contribution is to point out that this measure, which was formulated around 1897 by the pioneering statistician Karl Pearson, has well-behaved statistical properties which can be used easily by a court.

Tags: House · Politics · Redistricting

6 Comments so far ↓

  • 538 Refugee

    I can only guess the esteemed, gifted and often quoted mathematician Karl Rove prompted action by the Republicans in this instance?

    I just looked up the case and found an article suggesting this isn’t even about the numbers. They are disputing that the independent commission, even though the electorate voted it in via constitutional amendment is over ridden by the US constitution. An argument twice rejected by the court. Basically they are claiming the constitutional right to gerrymander?

    At least it puts your work out there for others to ponder if their situation is truly actionable.

    • Sam Wang

      Actually, I believe that article is about last year’s case challenging the existence of the Commission.

      Next month’s Harris case is nominally about whether GOP voters were packed into districts by the Commission, in violation of the “one man, one vote” principle. I am using it as a means of bringing up the question of whether there was actually any effect of the districting in terms of partisan asymmetry. The answer is no. If there’s no effect, this raises the question of whether there ought to be a remedy, which would be potentially disruptive to Arizona’s voters.

  • bks

    I had to read the ultimate sentence several times before I realized that the “Commission to Disadvantage Republicans” was not actually the name of a commission.

    Congrats on the document. Hoping that at least five of the SC justices are numerate.

  • Eric Walker

    Nothing to contribute except a deeply heartfelt Congratulations and fierce best wishes for success.

  • Geoff Brooks

    I’m delighted that you’ve done this Sam. This has the potential to change our democracy for the better.

  • Olav Grinde

    I am delighted to see this! It’s high time practices, and court decisions, be anchored in objective, quantifiable measures.

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